Refrigeration compressor capacity and loading control means



Aug. 30, 1966 K. v. VALBJQRN 3,269,645

REFRIGERATION COMPRESSOR CAPACITY AND LOADING CONTROL MEANS Filed Dec. 16, 196.3 2 Sheets-Sheet 1 M Pie ip P5 AP Ps' N. max

FIG 2 N mox W P PS b P5 P5 V FIG. 3

Aug. 30, 1966 r K. v. VALBJQRN 3,269,645

REFRIGERATION COMPRESSOR CAPACITY AND LOADING CONTROL MEANS Filed Dec. 16, 1963 2 Sheets-Sheet 2 United States Patent l 3,269,645 REFRIGERATION COMPRESSOR CAPACETY AND LOADENG ONTROL MEANS Knud V. Valbjrtrn, Nordborg, Denmark, assignor to Danfoss ved lug. M. Clausen, Nordhorg, Denmark, a company of Denmark Filed Dec. 16, 1963, Ser. N 3%,976 Claims priority, application Germany, Dec. 20, 1952, 1) 40,560 3 Claims. ((31. 230-22) This invention relates generally to refrigeration and air-conditioning compressors and more particularly to a new and improved compressor capacity and loading control means.

Hermetic refrigeration and air-conditioning compressors must be constructed for long operating lives of the component parts thereof which, of course, cannot be easily replaced. The construction of such compressors requires faultless operation under extreme working conditions. The construction of such compressors requires taking into consideration the relationship of capacity, suction temperature, condenser temperature, power output of the driving motor and operating speed thereof. Moreover, the refrigeration or air-conditioning load is generally subject to considerable variation during an operating period.

The construction of the compressor must take into consideration the highest and lowest evaporation temperatures and corresponding suction pressures at which the compressor is expected to work. The volume of the pressure strokes and number of compression strokes must be such that a sufiicient quantity of refrigerant is delivered rat a sufiiciently high pressure to allow liquifying it under these various operating conditions. On the other hand, the controlling factors in the construction of the motor driving a refrigerating compressor are governed by the highest evaporation temperature or the suction pressure corresponding to this temperature. The motor must deliver suflicient power to take care of the highest load it encounters. The motor must deliver the same amount of power at all time-s in units where provision is not made, by the use of motor controls, for variable power delivery by the motor. Thus, in order to maintain the motor output reduced and yet suflicient to drive the compressor at its highest operating suction pressure provision is generally made for loading control means by use of unloaders effective during the start of the compressor. These unloaders do not function as capacity control means.

A feature of a refrigeration compressor according to the invention is the provision of a compressor capacity and loading control means in which at least one cylinder port is provided in the individual compressor cylinders and a bypass valve for each of the individual ports is biased in a direction for closing a corresponding individual port and is operable to an operative position opening the port in response to pressure developed internally in the cylinder thereby to by-pass refrigerant in a gaseous state from internally of the cylinder to externally thereof, for example into a capsule of a hermetic compressor, during the inital phase of travel of the piston during a pressure or compression stroke. The bypass valve is biased to a closed position by a biasing spring constructed to permit the bypass valve to open the port for by-passing or discharging a fraction of the refrigerant from the cylinder to the exterior thereof only when pressure internally of the cylinder exceeds the biasing force of the spring during a phase of the compression stroke of the piston which is generally closer to the start of the individual compression stroke than to the end of the compression stroke thereby to control loading and capacity of "ice the compressor and to permit driving the compressor with less power input than would otherwise be required in the absence of the bypass valve.

The invention takes advantage of the fact that the weight of refrigerant delivered by the compressor increases with the increasing evaporation temperature on the one hand because of the higher suction pressure and on the other hand because of the higher density of the refrigerant. It is therefore possible to use a much smaller driving motor according to the invention than was heretofore possible. The motor is thereby cheaper and optimum compressor loading and capacity control are more easily maintained than heretofore.

The periods in which hermetic compressors operate at the maximum value of the evaporation temperature at which they are designed to operate are very rare particularly with respect to low and medium back pressure compressors. Compressors generally operate at their lower or medium evaporation temperatures. Thus provision has to be made for operating at the maximum value of the evaporation temperature and therefore high suction pressures. The capacity of the motor must provide for operating under maximum load conditions for the motor When the evaporation temperatures are highest. Thus during the usual operating conditions of such compressors the motor losses are considerable.

According to the invention the power output requirements of the motor can be decreased to such an extent that the range of power output of the motor provided corresponds substantially with the power requirements of the usual operating conditions and in those cases Where high suction pressures obtain the compressor capacity and loading control means according to the invention provides for unloading the cylinder so that the motor power is sufiicient for driving the compressor during compression of the gaseous refrigerant and the compressor will still deliver a sufiicient volume of refrigerant to have the compressor function properly.

Tests indicate that it is useful to not always bypass the same volume of refrigerant by unloading means if the suction pressure ju'stifies the use of an unloader. On the contrary, the volume of refrigerant being bypassed should bear a certain relation to the suction pressure, that is to say it should be greater or lesser according to Whether the suction pressure increases or decreases. This variable control, for example, can be accomplished in refrigerating apparatus by use of a throttle valve instead of a bypass valve. A throttle valve could, for example, vary the volume of the refrigerant unloaded or supplied with increasing suction pressure. Another possibility is keeping the cross-section area of a bypass valve or port constant, however, controlling the valve in such a way that its open time or period of time in which the valve is open to bypass or discharge refrigerant increases with increasing suction pressure.

This last-mentioned technique is realized by the invention in a simple arrangement by controlling a valve opening and closing a cylinder port, for example in dependence upon the difference between piston displacement pressure and suction pressure. This type of capacity and loading control is based on the fact that the pressure increases in the cylinder of a reciprocating compressor, for example, during a compression stroke as the suction pressure increases. Thus, by controlling a bypass valve and causing it to open sooner during a compression stroke as the higher suction pressure obtains the desired operating characteristics of the invention can be realized.

A feature of the invention as heretofore stated is the provision of a simple arrangement for carrying out compressor capacity control and cylinder loading by means of a simple form of a bypass valve comprising a spring loaded valve which closes a cylinder port and maintains it closed so long as a given suction pressure obtains or is not exceeded and when this suction pressure is exceeded the cylinder port is opened and maintained opened during a period of time proportionate to the increase of suction pressure relative to the first-mentioned given suction pressure which is a minimum suction pressure.

According to the invention, the bypass valve arrangement operates only during an initial phase of the compression stroke and its effectiveness is curtailed or otherwise rendered ineffective during the compression stroke as soon as the piston passes the cylinder port.

Another feature of the invention is the provision of a second valve port and valve which bypass refrigerant from internally of the cylinder to a space externally of the cylinder during the compression stroke for a period of compression sequential to the period in which the first mentioned valve bypasses refrigerant and is cooperative therewith. The second bypass valve is constructed so that it will not open unless a higher suction pressure exists than when the first-mentioned bypass valve operates or there is an increase in the difference between piston displacement or instantaneous compression pressure and suction pressure.

Other features and advantages of the capacity and loading control means according to the present invention will be understood as described in the following specification and appended claims, in conjunction with the following drawing in which:

FIG. 1 is a diagrammatic longitudinal section of a compressor cylinder provided with a bypass valve according to the invention and illustrates the corresponding compressor indicator diagram;

FIG. 2 is a diagram for illustrating the relationship of motor power and compressor suction pressure;

FIG. 3 is a diagrammatic longitudinal section of a cylinder of a compressor provided with a plurality of bypass valves according to the invention and illustrates diagrammatically a compressor indicator diagram or card for such a compressor;

'FIG. 4 is a sectional view of an embodiment of a compressor provided with bypass valve means according to the invention.

While the invention is particularly applicable to hermetically sealed refrigeration compressors and will be described as applied to hermetic reciprocating compressors those skilled in the art will recognize that the invention is equally applicable to reciprocating and other compressors for refrigeration and air conditioning apparatus which are not hermetically sealed.

According to the drawings, and more particularly to FIG. 1, in which a cylinder 1 of a reciprocating compressor, not shown, is illustrated diagrammatically as being provided with a valve plate 2. The valve plate is illustrated as a solid plate, however, it will be understood that it is provided with the usual intake and discharge valves for controlling intake and discharge of a gaseous refrigerant during the intake stroke and compression stroke of the piston 3 reciprocable in the bore 4 of the cylinder 1. The cylinder wall is provided with a port 5 having a fixed dimension or area and valve seat 7 circumferentially of the port and over which is disposed a pressure-actuated valve or plate 9 which is springbiased to a closed position by a spring 8. The loading or biasing spring 8 exerts a pressure or biasing force on the plate in a direction for seating the valve or plate on the seat 7 and closing the port. The pressure developed internally of the cylinder during the compression stroke of the piston 3 is exerted on the valve 9 in a direction for opening it. When the valve is open, it allows refrigerant in a gaseous condition to flow into a suction chamber illustrated diagrammatically as a space designated 6 externally of the cylinder for example a space internally of a cap sule, not shown.

The elasticity or biasing force of the spring 8 is AP. That is to say the suction pressure must rise from a given pressure to a higher pressure by an increase of pressure -P before the valve will lift during compression as later explained. During operating, for example, if the condenser pressure or pressure of the gas when compressed to a value necessary for liquification is P for example and a suction pressure is assumed to be P as illustrated in an indicator or p.-v. diagram corresponding to the operation of the compressor in FIG. 1, and the suction pressure P which has a lowest value for example a suction pressure P 1, the operation of the compressor is such that the pressure-volume diagram or indicator card having the ordinate "P for pressure and abscissa designated V designating the volume, is that illustrated in FIG. 1 resulting in a work curve I. The compressor thus functions in the usual manner at lower suction pressures. If the compressor is operating with a suction pressure P 1 the bypass valve 9 is not opened since the pressure developed internally of the cylinder during the initial phase of the compression stroke before the piston 3 moves past the part 5 is insufficient to overcome the resistance AP of the spring 8.

Assuming that the suction pressure increases an increment AP to a higher suction pressure P 2 then during the compression stroke and more particularly the initial phase thereof, the length of travel of the piston is designated a during this phase, an indicator card work curve III is de veloped. During this period of travel a or operation the bypass valve is pressure-actuated and opens so that gaseous refrigerant is discharged from the interior of the cylinder to externally thereof. In the absence of such bypass or controlled capacity and loading operation an indicator card curve II would be developed instead of an indicator curve III as illustrated on the indicator card. Thus from study of the indicator card or diagram of a compressor provided with bypass valve according to the invention it can be seen that the hatched area F under the curve 11 is representative of the amount of work or energy saved during each compression stroke. This is achieved in view of the fact that not only the absolute value of the compression pressure increases with the increasing suction pressure but also the speed or rate at which the compression pressure increases. During this operation the difference AP between piston displacement pressure or compression pressure and suction pressure which is suflicient to overcome the spring 8 of the bypass valve obtains at a time during which the piston has not yet closed off the valve port so that refrigerant is delivered from internally of the cylinder to the exterior thereof into the suction space. The interval or time during which the bypass valve functions to discharge gas refrigerant will increase as the suction pressure rises since the valve will lift proportionately sooner during a compression stroke.

From a study of the indicator card it is apparent that the limiting values of the suction pressure range at which the valve 9 becomes operative are indicated by the indicator card curves I and III and it can be understood that the time at which the valve 9 opens and therefore the refrigerant is bypassed varies from a zero value at the suction pressure P 1 to a respective value at suction pressure P 2 corresponding with the length of travel a. Thus the bypass valve constructed according to the invention not only achieves open-closed control thereby functioning as an unloader or loading control means in dependence upon the suction pressure but also control of volume and therefore capacity control in dependence of the suction pressure so that the unloading and capacity control of the compressor are obtained by the invention.

The power consumption N of a motor driven reciprocating compressor varies in dependence upon the suction pressure P as illustrated in FIG. 2. The power consumption curve N for a compressor without the provision of the invention is illustrated as the arc of the curve N and the are or portion of the curve illustrated in broken lines N and reaches a maximum value N max. The length of the arc N has a length b representative of the power consumption with respect to operating conditions, for example in which the evaporation temperatures are from minus twenty-five degrees to minus fifteen degrees centigrade. That is to say, the curve N is the power curve when the suction pressure is below P There is no difference in operation of known compressors and one provided with the invention in this range of operating pressures. However, as the suction pressure rises from P to P the power consumption curve in a compressor without the invention is that illustrated by the broken curve N which reaches a maximum value N max. The same type compressor provided with a bypass valve according to the invention has a power consumption curve N in this range of suction pressures as illustrated by a solid line and the power consumption reaches a maximum value illustrated as N max. Thus in studying the diagram of FIG. 2 it is apparent that by provision of the bypass valve according to the invention, the power consumption curve is varied only during those portions of the compression stroke in which the valve is unseated, as heretofore described and thereby the power consumption curve is greatly reduced. It can be seen, therefore, that in order to drive a refrigeration compressor provision of the bypass valve according to the invention permits a large reduction of the size of motor employed since less power input is required for driving the compressor.

Reciprocating compressors can be constructed according to the invention with a plurality of bypass valves, for example, as illustrated in FIG. 3 in which the same reference numerals are employed as in FIG. 1 in order to correlate and simplify the drawings. In FIG. 3 a cylinder 1 is provided with a valve plate 2 and a piston 3 is eci-procatory in the cylinder bore 4. The compressor is provided with a cylinder port 5 which is opened and closed by a bypass valve 9 biased to a closed position by the spring 8 having a resiliency AP as illustrated in a corresponding indicator card or diagram. The cylinder is provided with a second cylinder port 5 spaced axially apart from the firts-mentioned port 5 and open and closed by a bypass valve 9 biased to a closed position by a spring 8. The second spring 8' has less resiliency than the other spring 8 denoted as AP so that it begins to permit bypassing or discharge of refrigerant from internally of the cylinder to the exterior thereof only as a higher internal or compression pressure is reached, for example, due to higher ranges of suction pressure. The second bypass valve opens during a period of time subsequent to the blocking off of the port 5 by the piston 3 during a compression stroke so that the indicator diagram results in a curve IV is as illustrated in FIG. 3. The indicator card has a stepped curve as illustrated.

An embodiment of a hermetic compressor provided with capacity and loading control means according to the invention as illustrated in FIG. 4 as comprising a capsule 10 in which is disposed resilient mounting or suspension springs 11 for suspending an electric motor 12 for driving a reciprocating refrigeration compressor driven from an output shaft 13 of the motor provided with bearing means 14 and a cap 15 for driving reciprocably a piston 16 internally of a cylinder 17 provided in known manner with a valve plate 18 illustrated diagrammatically and cover 19. It being understood that the valves on the valve plates and the like are known and therefore are not illustrated.

The cylinder 17 is provided with structure 20 secured thereto defining a silencing chamber 21 in communication with the suction chamber 22 or inside space of the capsule by means of conduit means 23. Internally of the silencing chamber is provided a support clamp 24 for a flat spring 25 biasing a bypass valve 26 into a seated position on a seat 27 circumferentially of a cylinder port 28. The biasing force applied by the spring is adjustably set by a screw 29. The bypass valve functions as heretofore described with respect to the other embodiments in the figures of the drawing. When the valve is unseated the refrigerant is delivered into the chamber 21 which primarily functions as a silencer and attenuates the sound during the exit of the refrigerant from the valve 26 thereby to maintain the hermetic compressor silent for quiet operation. It will be understood, however, that the silencing chamber is not necessary for the invention to function and the chamber can thus be omitted. Moreover, the apparatus illustrated in FIG. 4 may be provided with a plurality of bypass valves as heretofore described.

Although the invention has been described with respect to a reciprocation compressor, for example a domestic hermetic compressor, it will be understood that it is not limited to reciprocatory compressors and the invention can be provided on other types of compressors, for example rotary and centrifugal compressors and reciprocating compressors which are not hermetic.

While preferred embodiments of the invention have been shown and described, it will be understood that many modifications and changes can be made within the true spirit and scope of the invention.

What I claim and desire to secure by Letters Patent is:

1. In a refrigeration compressor comprising a cylinder and a piston for sucking a gaseous refrigerant into the cylinder and compressing the gaseous refrigerant in the cylinder, compressor capacity and loading control means comprising means defining a first bypass port of constant area for bypassing refrigerant under pressure from interiorly of said compressor to exteriorly thereof, the pressure exteriorly of the compressor being the suction pressure, a first valve for opening and closing said first port, first resilient means constantly applying a biasing force on said first valve in a direction for closing said port and biasing said first valve against internal gaseous pressure in said compressor, said biasing force being less than the maximum opposing force exerted on said first valve by the pressure of the compressed gaseous refrigerant during a compression stroke of the compressor and greater than an initial suction pressure, said first port communicating between the interior and the exterior of the cylinder at a point which is on the compression side of the piston when the compression stroke has advanced to a point at which the opposing force exerted on said first valve by the pressure of the compressed gaseous refrigerant first exceeds said #biasing force and at which said first valve therefore opens said first port, said point of the compression stroke being before the end of the compression stroke, a second means defining a second bypass port of constant area for bypassing refrigerant under pressure from interiorly of said compressor to exteriorly thereof, said second port being disposed downstream of said first port, a second valve for opening and closing said second port, second resilient means constantly applying a biasing force on said second valve in a direction for closing said second port and biasing said second valve against internal gaseous pressure in said compressor, said biasing force of said second resilient means being less than the maximum opposing force exerted on said second valve by the pressure of the compressed gaseous refrigerant during a compression stroke of the compressor and greater than the opposing force exerted on said second valve by the pressure of the compressed gaseous refrigerant when the compression stroke has advanced to a point at which the compression side of the piston begin immediately adjacent to said first port, said second port communicating between the interior and the exterior of the cylinder at a point which is on the compression side of the piston when the compression stroke has advanced to a point at which the compression side of the piston is beyond said first port, whereby during a first stage of the compression stroke gaseous refrigerant escapes from the interior of the cylinder through only said first port, during a second stage of the compression stroke the escape of gaseous refrigerant through said first port is terminated and during a third stage of the compression stroke the escape of gaseous refrigerant through said first port remains terminated while gaseous refrigerant escapes from the interior of the cylinder through said second port.

2. In a refrigeration compressor according to claim 1, in which each of said resilient means comprises a spring.

3. In a refrigeration compressor according to claim 2, in which each of said valves comprises a plate biased against a respective one of said ports by a respective one 10 of said springs.

References Cited by the Examiner UNITED STATES PATENTS 774,503 11/1904 Yeakley 23028 877,492 1/1908 Doelling 23025 1,965,420 7/1934 Lipman 230-22 2,006,584 7/1935 De Puy 23022 2,260,113 10/1941 Frost 230-22 MARK NEWMAN, Primary Examiner.

W. I. KRAUSS, Assistant Examiner. 

1. IN A REFRIGERATION COMPRESSOR COMPRISING A CYLINDER AND A PISTON FOR SUCKING A GASEOUS REFRIGERANT INTO THE CYLINDER AND COMPRESSING THE GASEOUS REFRIGERANT IN THE CYLINDER, COMPRESSOR CAPACITY AND LOADING CONTROL MEANS COMPRISING MEANS DEFINING A FIRST BYPASS PORT OF CONSTANT AREA OF BYPASSING REFRIGERANT UNDER PRESSURE FROM INTERIORLY OF SAID COMPRESSOR TO EXTERIORLY THEREOF, THE PRESSURE EXTERIORLY OF THE COMPRESSOR BEING THE SUCTION PRESSURE, A FIRST VALVE FOR OPENING AND CLOSING SAID FIRST PORT, FIRST RESILIENT MEANS CONSTANTLY APPLYING A BIASING FORCE ON SAID FIRST VALVE IN A DIRECTION OF CLOSING SAID PORT AND BIASING SAID FIRST VALVE AGAINST INTERNAL GASEOUS PRESSURE IN SAID COMPRESSOR, SAID BIASING FORCE BEING LESS THAN THE MAXIMUM OPPOSING FORCE EXERTED ON SAID FIRST VALVE BY THE PRESSURE OF THE COMPRESSED GASEOUS REFRIGERANT DURING A COMPRESSION STROKE OF THE COMPRESSOR AND GREATER THAN AN INITIAL SUCTION PRESSURE, SAID FIRST PORT COMMUNICATING BETWEEN THE INTERIOR AND THE EXTERIOR OF THE CYLINDER AT A POINT WHICH IS ON THE COMPRESSION SIDE OF THE PISTON WHEN THE COMPRESSION STROKE HAS ADVANCED TO A POINT AT WHICH THE OPPOSING FORCE EXERTED ON SAID FIRST VALVE BY THE PRESSURE OF THE COMPRESSED GASEOUS REFRIGERANT FIRST EXCEEDS SAID BIASING FORCE AND AT WHICH SAID FIRST VALVE THEREFORE OPENS SAID FIRST PORT, SAID POINT OF THE COMPRESSION STROKE BEING BEFORE THE END OF THE COMPRESSION STROKE, A SECOND MEANS DEFINING A SECOND BYPASS PORT OF CONSTANT AREA FOR BYPASSING REFRIGERANT UNDER PRESSURE FROM INTERIORLY OF SAID COMPRESSOR TO EXTERIORLY THEREOF, SAID SECOND PORT BEING DISPOSED DOWNSTREAM OF SAID FIRST PORT, A SECOND VALVE FOR OPENING AND CLOSING SAID SECOND PORT, SECOND RESILIENT MEANS CONSTANTLY APPLYING A BIASING FORCE ON SAID SECOND VALVE IN A DIRECTION FOR CLOSING SAID SECOND PORT AND BIASING SAID SECOND VALVE AGAINST INTERNAL GASEOUS PRESSURE IN SAID COMPRESSOR, SAID BIASING FORCE OF SAID SECOND RESILIENT MEANS BEING LESS THAN THE MAXIMUM OPPOSING FORCE EXERTED ON SAID SECOND VALVE BY THE PRESSURE OF THE COMPRESSED GASEOUS REFRIGERANT DURING A COMPRESSION STROKE OF THE COMPRESSOR AND GREATER THAN THE OPPOSING FORCE EXERTED ON SAID SECOND VALVE BY THE PRESSURE OF THE COMPRESSED GASEOUS REFRIGERANT WHEN THE COMPRESSION STROKE HAS ADVANCED TO A POINT AT WHICH THE COMPRESSION SIDE OF THE PISTON BEING IMMEDIATELY ADAJCENT TO SAID FIRST PORT, SAID SECOND PORT COMMUNICATING BETWEEN THE INTERIOR AND THE EXTERIOR OF THE CYLINDER AT A POINT WHICH IS ONE THE COMPRESSION SIDE OF THE PISTON WHEN THE COMPRESSION STROKE HAS ADVANCED TO A POINT AT WHICH THE COMPRESSION SIDE OF THE PISTON IS BEYOND SAID FIRST PORT, WHEREBY DURING A FIRST STAGE OF THE COMPRESSION STROKE GASEOUS REFRIGERANT ESCAPES FROM THE INTERIOR OF THE CYLINDER THROUGH ONLY SAID FIRST PORT, DURING A SECOND STAGE OF THE COMPRESSION STROKE THE ESCAPE OF GASEOUS REFRIGERANT THROUGH SAID FIRST PORT IS TERMINATED AND DURING A THRID STAGE OF THE COMPRESSION STROKE THE ESCAPE OF GASEOUS REFRIGERANT THROUGH SAID FIRST PORT REMAINS TERMINATED WHILE GASEOUS REFRIGERANT ESCAPES FROM THE INTERIOR OF THE CYLINDER THROUGH SAID SECOND PORT. 